### Reevaluation of Fossil Indicates Lizards Are More Ancient Than Previously Assumed
Lizards, among the most primordial and enduring creatures on our planet, have intrigued researchers for ages. They flourished prior to the era of dinosaurs, endured the mass extinction event that eradicated their larger counterparts, and continue to thrive in modern times. Nevertheless, a recent reevaluation of a fossil indicates that lizards are even older than once thought, extending their origins by 35 million years. This revolutionary find offers fresh perspectives on the evolutionary journey of reptiles and calls into question earlier beliefs about their ancestry.
#### **The Finding of *Cryptovaranoides microlanius***
The fossil under discussion belongs to a minuscule lizard species identified as *Cryptovaranoides microlanius*, which existed roughly 205 million years ago during the late Triassic epoch. This tiny organism, whose name means “hidden lizard, small butcher,” probably predated on insects with its sharp teeth. Its remains were discovered in what is now southern England, a locale bustling with prehistoric wildlife during that era.
At first, the fossil was inaccurately classified as belonging to an archosaur, a class of reptiles that comprises dinosaurs, pterosaurs, crocodilians, and birds. However, a group of researchers from the University of Bristol recently reexamined the fossil and determined that *Cryptovaranoides* is not an archosaur but rather a lepidosaur. Lepidosaurs represent a broader category of reptiles that includes squamates, the classification that contains modern lizards and snakes. This reclassification positions *Cryptovaranoides* as the oldest known squamate, significantly reshaping our comprehension of reptilian evolution.
#### **What Establishes *Cryptovaranoides* as a Squamate?**
Researchers from the University of Bristol identified multiple skeletal characteristics that definitively categorize *Cryptovaranoides* within the squamate lineage. These characteristics, termed squamate apomorphies, are distinctive traits that arose later in their evolutionary history and differentiate them from their ancestral species. Notable features include:
1. **Forelimb Structure**: The humerus (the upper bone of the forelimb) and radius (the lower bone of the forelimb) of *Cryptovaranoides* showcase features such as the ectepicondylar and entepicondylar foramina, along with a radial condyle. These traits are commonly attributed to squamates and were either disregarded or misjudged in the original assessment.
2. **Cranial and Jaw Features**: The fossil exhibits a septomaxilla, a small triangular bone situated in the upper jaw near the nasal openings. This bone is a hallmark of squamates and was found in both the initial fossil and a subsequent larger specimen. Additionally, *Cryptovaranoides* does not feature a posterior projection on the jugal bone, a characteristic typical of squamates but missing in archosaurs.
3. **Dental Structures**: The lizard’s pleurodont teeth, which are attached to the jawbone rather than sitting in sockets, are a defining trait of squamates. The fossil also uncovered an unusual count of incisive teeth—seven in total—further distinguishing it from archosaurs.
4. **Choanal Sulcus**: The choanae, or openings at the posterior part of the nasal cavity, display a depression (sulcus) that gradually becomes less pronounced towards the back. This pattern aligns with contemporary squamates and contrasts with other reptilian groups.
5. **Occipital Recess**: The posterior part of the braincase in *Cryptovaranoides* contains a sizable hollow area known as the occipital recess. This feature appeared in squamates during the late Triassic and early Jurassic periods, further validating the fossil’s identification as a squamate.
#### **Significance for Reptilian Evolution**
The reclassification of *Cryptovaranoides microlanius* as a squamate carries major implications for our understanding of reptilian evolution. Establishing that squamates existed 205 million years ago shifts the timeline for the group’s origins back by 35 million years. It also indicates that squamates were already undergoing diversification during the late Triassic, an era characterized by significant ecological shifts and the emergence of dinosaurs.
These findings position *Cryptovaranoides* within the crown group of squamates, meaning it is part of the earliest clade that has descended from a shared ancestor, encompassing all modern lizards and snakes. This reclassification highlights the necessity of revisiting and reanalyzing fossils, as advancements in technology and new viewpoints can result in transformative discoveries.
#### **Challenges and Future Investigations**
While the Bristol group is confident in their findings, they recognize the need for additional studies of the *Cryptovaranoides* holotype and associated fossils to enhance our understanding of its anatomy and evolutionary role. However, they firmly maintain that the fossil is “undoubtedly a lepidosaur and a squamate.”
